1. Field of the Invention
The present invention relates to a catalyst for the polymerization of olefins, a solid catalyst component utilizable for the catalyst and a process for the preparation of such catalyst component. More particularly, the present invention relates to a solid catalyst component derived from a dialkoxymagnesium, a diester of an aromatic dicarboxylic acid, a halogenated hydrocarbon and a titanium tetrahalide, a catalyst obtained from the solid catalyst component, a piperidine derivative and an organoaluminum compound and useful for the production of stereoregular olefin polymers in a higher yield, and a process for the preparation of the solid catalyst component by contacting the above ingredients in a specific order of succession.
2. Description of the Prior Art:
From the past, a number of Ziegler type catalysts derived from a combination of a titanium halide and an organoaluminum compound are widely known and used for the polymerization of olefins. In the polymerization of olefins by the aid of such catalyst, however, the yield of polymers per solid catalyst component or titanium contained therein (referred to hereinafter as the polymerization activity per solid catalyst component or titanium contained therein, respectively) is low so that the step for eliminating the catalyst residue, i.e. the deashing step is necessary after the polymerization step. Since such deashing step requires a large amount of an alcohol or a chelating agent, facilities for recovering or regenerating the solvent or chelating agent are necessary in the commercial process, thus creating a problem of resource, energy and incidental factors. Thus, there were many key problems to be solved immediately in the prior art processes for polymerization of olefins. Since then, extensive research has been carried out to omit such tremendous deashing treatment thereby enhancing the polymerization activity per solid catalyst component, especially per titanium contained therein.
According to the recent tendency, a number of proposals have been presented wherein a transition metal compound as active ingredient, such as a titanium halide, is supported on a carrier such as magnesium halide with an attempt to increase the polymerization activity per titanium in the catalyst component significantly in case of being used for the polymerization of olefins. However, the processes recently proposed have also such drawbacks that chlorine contained in the magnesium chloride chiefly used as the carrier as well as a halogen atom contained in the titanium halide have a negative influence on the resultant polymer. In these processes, therefore, a problem still remains unsolved in that the activity demanded is decreased to a level at which the influence of chlorine is almost negligible, or alternatively, the concentration itself of chlorine has to be reduced.
With a view to minimizing the residual chlorine in the polymer produced, a process aiming at decreasing the amount of the residual chlorine in the polymer while maintaining a high polymerization activity per solid catalyst component and a high yield of stereoregular polymer was developed and disclosed in Japanese Laid-open Patent Appln. No. Sho. 59-91107.
Generally, on the polymerization of olefins in an industrial scale, especially in the commercial production of stereoregular polymers from propylene, butylene-1 or the like olefins, with the aid of a polymerization catalyst containing magnesium chloride as a support, it is usually indispensable to allow an electron donor such as an ester of an aromatic carboxylic acid to be co-existent with the catalyst in the polymerization system. However, the presence of such ester in the polymerization system raises a new problem as the ester imparts its peculiar esteric odor to the resultant polymer.
What is more, a serious problem arises in the use of such catalyst. In the so-called supported catalysts, such as a catalyst containing magnesium chloride as a support, the activity at the initial stage of polymerization is certainly high but is considerably deactivated with the lapse of time, thus incurring a problem in process operations. Consequently, the use of the catalyst of this type is substantially impossible for the purpose of block copolymerization where a relatively longer polymerization time is required. To improve this drawback, a modified process is disclosed, for example, in Japanese Laid-open Patent Appln. No. Sho. 54-94590 wherein a magnesium dihalide is treated with an electron donor and a tetravalent titanium compound optionally with an electron donor, and then the resultant product is combined with an organoaluminum compound, an ester of an aromatic carboxylic acid and a compound of the formula: M-O-R (wherein M is a metal belonging to the Groups I-A, II-A, II-B, III-A, III-B, IV-A and IV-B of the Periodic Table and R is hydrogen or a hydrocarbyl group) to form a catalyst for the polymerization of olefins. In this process, the catalyst is not satisfactorily prevented from deactivation, and moreover, the problem of "odor" in the resultant polymer is not as yet solved since the ester is used together with the catalyst on polymerization of olefins. Further, the preparation of the catalyst and the polymerization method according to this process requires a troublesome and complicates operations as described in Example I(A), (B) and (C) given in the specification of this reference. Thus, the catalyst proposed in this reference is slightly improved in the catalyst performance but does not reach a practically satisfactory level in both catalytic performance and maintenance of activity.
In Japanese Laid-open Patent Appln. No. Sho. 58-138706, there is disclosed a process for the polymerization of olefins with the aid of a specific catalyst which is derived from a highly active catalyst component containing magnesium, titanium, halogen and an electron donor, an organoaluminum compound, and a heterocyclic compound or a branched alkyl-containing ketone. In this catalyst, the electron donor is an ester of a polybasic carboxylic acid such as a dialkyl phthalate or an ester of a specific branched chain- or ring-containing monocarboxylic acid such as trimethylacetic acid, while the heterocyclic compound is an .alpha.,.alpha.'-di-tri- or -tetrasubstituted heterocyclic compound such as 2,6-disubstituted or 2,2,6,6-tetrasubstituted pyran or piperidine. According to this process, the yield of stereoregular polymer is enhanced to a certain degree and the aftertreatment usually necessary for eliminating residual catalyst can be omitted. However, the magnesium compound actually used in the catalyst component in all Examples is only magnesium chloride although the compound is broadly defined so that it may be an alkoxymagnesium halide or even an alkoxymagnesium. Furthermore, the reaction condition for preparing the catalyst is extremely troublesome and complicated, especially in controlling the temperature, as is evident from Examples 1-4 of this reference.
In U.S. Pat. No. 4,414,132, there is disclosed a polymerization catalyst for olefins and a process for preparing the same wherein the catalyst is obtained by combining an organoaluminum compound and a selectivity control agent with a solid component which has specifically been prepared by halogenating a magnesium compound such as diethoxymagnesium with a titanium tetrahalide in the presence of a halohydrocarbon and an electron donor which may be identical with the selectivity control agent, and then contacting the halogenated product with a titanium tetrahalide. Namely, the gist of this patent resides in the use of a specific solid component prepared in a specific manner from the magnesium compound, the titanium halide and the electron donor. According to Example 2 of this patent illustrating the preparation of the solid component, a dialkoxymagnesium is suspended in carbon tetrachloride, ethyl benzoate as a preferable electron donor and titanium tetrachloride are added to the suspension at 75.degree. C. and the mixture is stirred for 2 hours while maintaining the temperature at 75.degree. C. The resultant solid is once isolated, washed 5 times with iso-octane to form a solid (Component a). This solid is further suspended in titanium tetrachloride at 80.degree. C. and the suspension is subjected to stirring for 2 hours whereupon a solid formed is separated and washed 5 times with iso-octane to form a solid component (Component b). The resultant component is combined with triethylaluminum and p-methoxybenzoic acid ethyl ester (the most preferable selectivity control agent) to form a catalyst for the polymerization of olefins, as illustrated in Example 1. In this process, however, a preferable electron donor which also functions as the selectivity control agent is an ester of an aromatic monocarboxylic acid. According to the process of this patent, the polymerization activity of the catalyst and the yield of stereoregular polymer are certainly improved but do not still reach a satisfactory level desired in the industrial scale production of olefin polymers. In particular, maintenance of the activity against deactivation is scarcely improved in the catalyst of this patent.
Under the above circumstances, therefore, there is a great demand for developing a new catalyst for the polymerization of olefins which is remarkably improved in any of the polymerization activity, stereospecific performance and maintenance of the activity to a satisfactory level in the actual commercial scale production of stereoregular olefin polymers in a high yield.